The present invention pertains to a test signal generator. More particularly, the present invention pertains to a circuit for generating signals for testing a brake controller for a railroad car.
Railroad cars generally are equipped with a truck at each end, each truck having two axles with a wheel on each end of each axle. The two wheels of an axle turn together as a set, but each axle of a truck is independent, and, of course, the two trucks are independent. Thus, each axle of a railroad car rotates independently of the other three axles of that car and independently of all the axles of other cars.
When it is necessary to slow or stop a railroad car, the pneumatic brakes of the car are applied. Maximum braking occurs when the wheels are braked to a point just before slipping of the wheel on the railroad track. Slipping of the wheels on the track is undesirable primarily because such slipping results in less than maximum braking. Additionally, slipping is undesirable because it causes wear on that spot of the wheel at which the slipping occurs, producing a "flat" on the wheel.
Slipping of a wheel can be sensed either as it occurs or just prior to occurrence by sensing the speed of the wheels. First of all, comparison of the speed of the wheels of one axle of a railroad car with the speeds of the wheels of the other three axles of that same railroad car indicates whether the four axles are stopping at the same rate. Excessive speed differences indicate abnormal braking. Secondly, sensing the rate of stopping or deceleration of the wheels of an axle indicates whether the wheel is decelerating so rapidly as to indicate slipping.
Generally railroad cars are equipped with devices which sense these wheel conditions and control the application of pneumatic pressure to the brakes. Thus, for example, the E-5 Decelostat Controller System available from Westinghouse Air Brake Company senses the speed of each of the four sets of wheels of the railroad car and from those speeds determines whether slipping is indicated. Thus, the E-5 Decelostat Controller System has four input circuits so that it receives simultaneously a speed signal from each of the four axles of a railroad car. The equipment makes two different comparisons of wheel speed. First of all, the equipment compares the speeds of each of the four sets of wheels, and if the speed of any of the four sets of wheels differs from the speed of any other set by an amount indicating that one set is slipping while the other set is not, the equipment generates a signal to release the pneumatic pressure for the brakes on the truck of the slipping wheel. Secondly, the equipment senses the rate of deceleration of each set of wheels, and if any set of wheels is decelerating at so high a rate as to indicate slipping, the equipment likewise generates a signal to release the pneumatic pressure for the brakes of the associated truck.
Accordingly, the safe braking of railroad cars is dependent upon proper operation of the controller. It is thus necessary to be able to test the controller to assure that it is operating properly.